The main reason MS do it is that it's cheaper to support only one OS, that being the newest one.
Having security experts code fixes for Windows 7 etc is expensive. This
is why they kind of gave away Windows 10 for win7 users its ultimately
just cheaper easier for MS.
I too am still on the X58 platform, I used to have an i920 but I bought a
1366 X58 compatible Xeon hex-core X5575 CPU for $45AUD and overclocked
the crap out of it to 4.6Ghz
I too installed windows 10 on a newly installed SSD on my X58 but
conversely what I love about Windows 10 is that I haven't had to install
any drivers, Win10 detects everything perfectly, no driver downloads.
No driver problems, no instability problems.